Part I. An Overview of the Bicycle Study

Transcription

1 Part I. An Overview of the Bicycle Study Gregory B. Rodgers, Ph.D. Bicycle Project Manager, Directorate for Economic Analysis Background Bicycle riding is one of the most popular recreational activities in the United States. The National Sporting Goods Association (1992) estimates that bicycle riding was the third leading U.S. recreational activity in 1991, after exercise walking and swimming. In addition, bicycle riding is an important means of transportation. The Bicycle Institute of America (1993) estimates that there were about 4.3 million Americans who regularly commuted to work in Bicycle riding is also a risky activity, as indicated by the large numbers of injuries and deaths involving bicycles every year. According to the U.S. Consumer Product Safety Commission's (CPSC) National Electronic Injury Surveillance System (NEISS), an injury reporting system that consists of a statistical sample of the nation's hospital emergency rooms, there have been about one-half million nonfatal bicycle-related injuries treated in hospital emergency rooms every year since the early 1970s, when NEISS became operational. When other medically-attended injuries are counted, such as injuries treated in physicians' offices, there may be on the order of one million medically-attended injuries involving bicycles every year. In addition, there are as many as 1,000 bicycle-related fatalities annually. The estimated costs of these injuries and deaths to society are high -- approximately $8 billion annually -- and suggest that injury reduction strategies with even modest levels of effectiveness could prove to be cost-effective. The CPSC has long had an interest in bicycle-related hazards and in promoting bicycle safety. The agency began development of a mandatory standard for bicycles as one of its first orders of business in The bicycle standard, which became effective in 1976, 1 set safety requirements for reflectors, wheels and tires, chains, pedals, braking and steering systems, and for structural components such as frames and forks. More recently, the Commission has provided a substantial amount of information on bicycle safety to the public and encourages all riders to use helmets. 1 See, 16 CFR Part 1512, 41 Federal Register , January 28, 1976, and 16 CFR Part 1512, 43 Federal Register , December 22,

2 Bicycle safety is also promoted by many other governmental and non-governmental organizations, and is of considerable interest to the health and safety research community. In 1991, Congress passed the Intermodal Surface Transportation Efficiency Act (ISTEA), an act that required all states and metropolitan planning organizations incorporate programs and facilities for bicyclists in their transportation plans. Also in 1991, the Department of Transportation's (DOT) Appropriations Act instructed DOT to develop a plan to promote bicycling and walking, and to enhance the safety of these transportation modes. The interest of the health and safety community in bicycle safety is evidenced by the large number of professional publications in the safety and medical literature. For the most part, however, the published literature on bicycle hazards consists of injury analyses carried out at the level of the individual hospital or in limited geographical areas. While these studies provide valuable information about injury characteristics in various localities, there has never been a comprehensive national study of bicycle use and hazard patterns designed to quantify riding patterns and the rider and environmental factors associated with risk. Moreover, while injuries resulting from bicycle-motor vehicle collisions have been evaluated extensively (Cross and Fisher, 1977; Roland et al., 1979), little attention has been given to the analysis of bicyclerelated hazard patterns which do not involve motor vehicles, but which do account for the great majority of injuries. The CPSC bicycle project was intended to remedy some of these data deficiencies by evaluating bicycle use and hazard patterns on a national basis. The remainder of this report provides an overview of the methodology of the bicycle study, and the study findings. Data and Methods The CPSC conducted two nationwide bicycle surveys in The first, the "injury survey," was conducted by the CPSC's Directorate for Epidemiology (EP) during calendar year 1991 and gathered information on a sample of 463 bicycle-related (nonfatal) injuries reported through NEISS. NEISS injury reports were followed up with telephone interviews to collect information on the characteristics and use patterns of riders with injuries treated in hospital emergency rooms, the types of injuries suffered, and descriptions of the injury and hazard scenarios. EP identified 41 incidents (i.e., injury accidents reported through NEISS) which might have involved mechanical failure or design problems. These incidents were assigned for on-site investigations. The Directorate for Engineering Sciences (ES) evaluated these incident investigations to determine if there were systematic mechanical hazards which might be addressed by revisions to the existing mandatory standard. The second survey, the "exposure survey," was a national random-digit-dial telephone survey that collected information on the characteristics and use patterns of the general population of bicyclists. The survey was conducted by Abt Associates, Inc., under the 2

3 direction of the Directorate for Economic Analysis (EC). It resulted in 1,254 completed interviews with bicyclists from around the nation. These surveys provided nationally representative samples of injured bicyclists who were treated in hospital emergency rooms and of the general population of bicyclists. Because they gathered parallel information on injured and noninjured bicyclists, the agency staff were able to conduct a "risk analysis" by comparing the characteristics and use patterns of injured riders with those who were not injured. In effect, the exposure data were used as "control data" against which to compare the characteristics and use patterns of injured bicyclists. The aim of the risk analysis was to determine and quantify the rider and environmental factors associated with higher risk levels. The Division of Human Factors (HF) reviewed the injury and exposure survey data bases in light of behavioral studies applicable to bicycle riding. HF also evaluated the literature on bicycle safety education and training, with emphasis on the developmental capabilities of children. The CPSC does not collect information on all bicycle-related deaths. However, because deaths constitute an important bicycle hazard pattern, the study provides a brief description and analysis of information on bicyclist deaths obtained from the National Center for Health Statistics and from the National Highway Traffic Safety Administration's (NHTSA) Fatal Accident Reporting System. To complement the analysis of bicycle use and risk patterns, the agency purchased data from a comprehensive 1990 survey of adult bicyclists commissioned by Rodale Press, the publishers of Bicycling magazine (Rodale Press, 1991). The Rodale Press survey was conducted by National Family Opinion, Inc., from its national consumer mail panel, and included interviews with over 3,200 adult bicyclists who were 18 years-of-age and older. Although the survey did not gather information on bicycle use by children, a major focus of the CPSC project, it did gather data on a wide range of topics relevant to an analysis of the risk and safety behavior of adult bicyclists. In many cases, its results were directly comparable to the results of the CPSC exposure survey. It also provided market data, such as plans for future purchases of bicycles and equipment, which were unavailable from other sources. Characteristics of Riders and Injury Statistics This section summarizes some of the important descriptive results from the 1991 injury and exposure surveys, including the characteristics and use patterns of riders, and injury statistics. Rider Characteristics and Use Patterns The results of the exposure survey are detailed in Part II. The exposure survey confirmed the popularity of bicycle riding in the U.S. There are about 67 million bicyclists 3

4 who ride a total of about 15 billion hours annually. Most bicycle riding is for recreational purposes, but almost 9 percent of riders use their bicycles primarily for commuting to work or school. Just over half of all bicyclists (52 percent) are males. In addition, a large proportion of bicyclists are young. About 22 percent are under the age of 10 years and 40 percent are under age 15. Young bicyclists ride more than the average for all bicyclists. Riders under age 15 reportedly ride about 300 hours per year, about 50 percent more than the average reported for riders age 15 and older. Most bicyclists (64 percent) ride a substantial proportion of the time on neighborhood streets with low traffic volume, but sizable proportions also spend a lot of their riding time on sidewalks and playgrounds (29 percent), bike paths (17 percent), and unpaved roads (18 percent); smaller proportions ride on major thoroughfares with high traffic volume (7 percent) and on other unpaved surfaces or trails (11 percent). Children under age 10 ride primarily on sidewalks, playgrounds, and neighborhood streets; riders over age 10 are more likely to be found on neighborhood streets, bike paths, or major thoroughfares. About 12 percent of bicyclists ride at least occasionally after dark. However, less than one-third of these nighttime riders use headlights or taillights. There are about 96 million bicycles in existence, but only about 66 million (69 percent) were used in the year prior to the survey. Children's models (i.e., sidewalk or BMX/high rise) account for over one-fourth of the bicycles in use. Of the adult models (i.e., lightweight racing/touring, mountain, and middleweight/cruisers), the lightweight racing and touring bicycles are the most common and account for about one-third (34 percent) of the bicycles in use. Mountain bikes were first marketed in substantial numbers in the early 1980s, and now account for about 17 percent of the bicycles in use. 2 The Rodale Press survey findings for adult bicyclists (age 18 and over) are described in Part VII of the study. They are generally consistent with the findings of the CPSC exposure survey. The majority of adult bicyclists (62 percent) rode most often on neighborhood streets. In addition, over half (57 percent) had access to community bike paths, and 28 percent had access to extra wide roads or bike lanes. Many bicyclists said that "having safer places to go riding" (35 percent) or "being able to ride to work" (14 percent) would encourage them to ride their bicycle more often. About one-fifth of the Rodale Press survey respondents expected to purchase a new bicycle within 2 years. The mean expected outlay was $334, an 82 percent increase over the mean price paid ($183) by recent purchasers. The Rodale Press results also indicate that 2 The term mountain bike refers to the class of bicycles that includes city, all-terrain, or mountain bicycles. 4

5 mountain bicycles are increasing in market share. While 14 percent of recent purchasers said that they had bought a mountain bicycle, 44 percent of those planning a purchase expected to buy a mountain bicycle. Characteristics of Victims, Injuries, and Injury Location According to the analysis of the injury survey results, which are detailed in Part III of the study, there were an estimated 588,000 bicycle-related injuries treated in U.S. hospital emergency rooms in About 531,000 (90 percent) involved bicycle operators; the remainder involved primarily passengers and bystanders. About 62 percent of the injured operators were male. Most were also children: about 37 percent of the injured operators were under age 10, and 71 percent were under age 15. Non-operators who were injured (i.e., primarily passengers and bystanders) were younger than injured operators; about 66 percent of the injured non-operators were under age 10. Injured bicycle operators also tend to be younger than the general population of bicycle riders. Table 1 compares the ages of injured operators with those of the general rider population from the exposure survey. As can be seen, children between the ages of 5 and 14 are disproportionately involved in accidents resulting in injury. While 5-to-14 year-old bicyclists represent about 36 percent of riders, they account for about 68 percent of all emergency room treated injuries. Table 1: Distributions of Riders by Age Age Injured All Operators Riders (years) (Percent) (Percent) # $ Total Source: 1991 CPSC Bicycle Injury and Exposure Surveys. Almost one-third (30 percent) of all operator injuries involved the head or face; 27 percent of these head/face injuries involved potentially serious diagnoses, such as fractures, internal injuries, or concussions. Young children suffered a significantly higher proportion of head injuries than older victims; 50 percent of the injuries suffered by children under age 10 involved the head or face, compared with 19 percent for riders age 10 or older. 5

6 Less than 3 percent of injury victims were admitted for hospitalization. This is about the same rate of hospitalization (about 4 percent) for all product-related injuries reported through NEISS in Just over half of the operator injuries (53 percent) happened on roadways (i.e., surfaces designed for use by motorized vehicles). About three-quarters of the roadway injuries occurred on neighborhood streets; the remainder were on major thoroughfares and unpaved roads. Riders age 25 and older were injured on highways or major thoroughfares more frequently than younger riders. Bicyclists under age 25 who were injured on roadways were more likely to be injured on neighborhood streets. Another 12 percent of the operator injuries occurred on sidewalks and playgrounds; most involved children under age 10. About 5 percent of the incidents occurred on unpaved roads, 5 percent occurred on trails, and less than 1 percent occurred on bike paths. Injury Hazard Patterns and Risk Factors A major focus of the bicycle study was the evaluation of bicycle hazard patterns and the bicycle risk analysis. This section summarizes the results of these analyses, which are contained in Part III of the study. It also presents some complementary results from a risk analysis of the Rodale Press survey data base, which can be found in Part VIII. Hazard Patterns and Contributing Factors. 3 An estimated 15 percent of the injuries involved collisions with moving objects, such as motor vehicles, other bicycles, or animals. Another 13 percent involved collisions with nonmoving objects, such as parked cars, traffic signs, or fences. Incidents involving collisions or near-collisions (i.e., swerving to avoid collisions) with moving motor vehicles accounted for only about 10 percent of the injuries. About 11 percent of the incidents occurred while victims were performing stunts, such as jumping over ramps or speed bumps, or performing "wheelies." About 88 percent of the incidents that occurred while performing stunts involved children under age 15, and 80 percent involved male riders. Respondents reported a number of factors that contributed to the incidents. Uneven riding surfaces (e.g., bumps, ruts, curbs) contributed to about 27 percent, slippery surfaces contributed to about 15 percent, and "going too fast" contributed to about 22 percent. Other miscellaneous reported factors included mechanical failure, rider inexperience, inattention, 3 Unless otherwise noted, all injuries refer to injuries suffered by bicycle riders (i.e., bicycle operators rather than passengers or bystanders). 6

7 riding the wrong size bicycle, or riding at night without a light. The use of earphones or carrying young children in child carriers did not play a major role in injury scenarios. Just over one-fifth of the injuries occurred under non-daylight conditions: about 5 percent were at night and 16 percent were at dawn or dusk. However, about 35 percent of the injuries on major thoroughfares occurred under non-daylight conditions. Less than 3 percent of the injuries occurred in rain or snow. Risk Analysis and Risk Factors Table 2 presents information on injury rates for various age groups. Based on the results of the injury and exposure surveys, there were about 8.8 bicycle-related injuries treated in hospital emergency rooms for every 1,000 riders in Riders 5-to-14 years of age have the highest injury rate with about 17 injuries per thousand riders. The injury rate for all riders age 15 and older is considerably lower than the child injury rate. However, when adjusted for hours of annual use, the injury rate for riders over age 64 is similar to the child injury rate. Although based on a small sample of older riders, riders over the age of 64 (who ride much less than children) have an adjusted injury rate comparable to that of riders in the 5-to-14 yearold age group. Table 2: Bicycle Injury Rates, by Age Group Victim Injuries per Injuries per Age Thousand Million (years) Riders Hours of Use All Ages # $ Source: 1991 CPSC Bicycle Injury and Exposure Surveys EP staff used a logistic regression model to determine and quantify the factors associated with the injury risk. 4 They estimated a general model which included riders from all age groups. In addition, they estimated two separate risk models, one for riders under age 15 ("children"), and one for riders 15 years of age and older ("adults"), because of the significant risk differential between these two groups. 4 This statistical technique is used to determine the independent impact of each of several factors on the injury risk. It is useful when a number of factors simultaneously affect the injury risk. 7

8 The general model found a significantly higher risk for children under age 15. Holding all other factors constant, the risk for a child under age 15 was over 5 times the risk for an older rider. Most of the other results for the two age-specific models were similar to those in the general model. In the children's model, higher risks were associated with certain riding surfaces, time of day, and population density. Children who rode during non-daylight hours, on streets, and who lived in areas with greater population density were more likely to be injured. The risk on streets was about 8 times the risk on bike paths, 3.4 times the risk on unpaved surfaces, and about 1.7 times the risk on sidewalks. Riding under non-daylight conditions (e.g., at night, dusk, or dawn) was about 3.6 times more risky than riding during the daytime. Rider gender had no statistically significant effect on the injury risk. In the model for riders 15 years of age and older, risk was also affected by riding surface. As in the children's model, the adult risk was higher on paved roadways. The risk on neighborhood streets was about 7 times the risk on bike paths and about 9 times the risk on unpaved surfaces. Moreover, the risk on major thoroughfares, the highest risk riding surface, was about 2.5 times the risk on neighborhood streets. As in the children's model, risk was higher for riders who lived in areas with greater population density. However, there was no significant difference in risk between daylight and non-daylight hours. Nor did rider gender independently affect the injury risk. In the Rodale Press survey of adult riders, about 9 percent of respondents reported that they had had accidents in which they had crashed or fallen off their bicycle within 12 months of the survey. These accidents may or may not have resulted in a medically-attended injury. An analysis of factors associated with this accident risk was highly consistent with the results of the EP risk analysis of riders 15 years of age and older. One especially noteworthy finding was that the accident risk rose for riders over age 64; the risk for riders over age 64 was significantly higher than for riders 25-to-64 years of age. (This finding was suggested in the EP risk analysis, but was not significant, probably because of the small sample of riders over age 64.) In addition, the accident risk was substantially higher on off-road trails (a type of riding surface not evaluated directly in the EP risk assessment) than on other riding surfaces. 5 Human Factors Evaluation of Children's Risk HF reviewed the bicycle injury data on children and the existing literature on safety education and training. This analysis, which can be found in Part IV, provides some explanation for the higher risks for children under age 15, based primarily on the cognitive immaturity of children. According to HF, bicycle riding is a complicated activity in which a lot 5 Riding on "unpaved roads" was combined with "other unpaved surfaces and trails" in the EP risk analysis. 8

9 of information is vying for the attention of children. Children often do not have the ability to filter all the information, or to filter it correctly. According to available literature, children 5-to-14 years of age begin to test their skills and experience many physical and cognitive changes. They may push their bodies physically in ways that can lead to injury. In addition, boys tend to be more risk-taking than girls, as evidenced in many studies. These factors may help explain why 88 percent of those injured while performing stunts were under age 15, and why 80 percent involved boys. The egocentric behavior of children (i.e., the inability to perceive other people's viewpoints) also helps explain their higher injury risk. It is not until around the age of 10 that children are able to consider the consequences of their actions. For example, children under age 10 may not consider their behavior unexpected when they suddenly turn in front of a car or dart out of a driveway, because that appears to them as the only way to go. Evaluation of Mechanical Hazards EP identified 41 incidents (i.e., injury accidents reported through NEISS) which might have involved mechanical failure or design problems. These cases represented about 13 percent of the operator injuries, and were all assigned for on-site investigations. ES evaluated the incident investigations to determine if there were systematic mechanical hazards which might be addressed by revisions or amendments to the existing mandatory standard. This analysis can be found in Part V. The most frequently reported problems involved bicycle chains breaking or falling off, brakes failing, and various components such as handlebars and brake components coming loose. By mechanical component group, the 41 cases involved: brakes (15 cases); chains (13 cases); handlebars (6 cases); tires (2 cases); and gear cables, seats, spokes, handgrips, and pedals, with one case each. Although the cause of these alleged mechanical failures could not be absolutely determined, ES concluded that poor bicycle maintenance and/or bicycle modifications were contributors in a minimum of 9 cases and possible contributors in an additional 11 cases. External conditions, such as slick road surfaces, were probable contributors in 4 cases. In addition, operator behavior and unfamiliarity with a bicycle were described as possible contributors in 12 cases. Only 15 of the cases (representing an estimated 4 percent of emergency room treated injuries) reported component malfunctions without indicating other likely contributing factors. However, information was insufficient to determine if these incidents resulted from inherent mechanical failure not attributable to poor maintenance, ill-advised modifications, or other factors. ES concluded that there were no significant mechanical failure patterns that warranted amendment or revision to the mandatory bicycle standard. 9

10 Bicycle-Related Deaths Information on bicycle-related deaths is available from two sources: the National Center for Health Statistics (NCHS) and NHTSA's Fatal Accident Reporting System (FARS). In Part III of the study, NCHS data on deaths are discussed and compared to data from the injury survey. The NCHS identified about 890 bicyclist deaths in 1989, the most recent year for which data from that source are available. About 90 percent of the deaths involved motor vehicles, compared to about 10 percent of the nonfatal injuries treated in hospital emergency rooms. According to the NCHS data, bicycle injury victims who died tended to be older than those who were treated for nonfatal injuries in hospital emergency rooms. As shown in Table 3, about 63 percent of those who died were age 15 or older, and about 17 percent were age 45 or older. In contrast, about 29 percent of the nonfatal injury victims were age 15 or older, and only about 4 percent were age 45 or older. In addition, fatal accidents were more likely to involve males. About 85 percent of the fatality victims were male, in contrast to about 62 percent of the nonfatal injury victims. Table 3: Age and Gender of Victims, by Percent of Deaths and Injuries Deaths Injuries (NCHS, 1989) (NEISS, 1991) Age (years) (Percent) (Percent) # $ Total Gender Female Male Total Source: National Center for Health Statistics 1989, and the 1991 CPSC Bicycle Injury Survey Fatal injuries also tended to involve a greater proportion of head injuries than did nonfatal injuries treated in hospital emergency rooms. While the injury survey indicated that 30 percent of emergency room treated injuries involved the head or face, Sacks et al. (1991) estimated that about 62 percent of all bicycle-related deaths involved head injury. In Part VI of the study, bicycle-related deaths reported through NHTSA's Fatal Accident Reporting System (FARS) are evaluated in conjunction with data from the exposure 10

11 survey. The FARS data are limited to deaths resulting from crashes with motor vehicles on public roadways (about 90 percent of deaths), but since data were available for 1991, the FARS data were directly comparable to data from the 1991 exposure survey. It was therefore possible to estimate comparative risk factors for various gender and age categories by comparing the distribution of the 1991 FARS deaths with estimates of riding exposure from the 1991 CPSC exposure survey. This analysis revealed that the fatality risk for male bicyclists, adjusted for riding exposure, was almost five times the risk for female bicyclists. In addition, when adjusted for exposure, the fatality risk for 16-to-24 year-old bicyclists was about 2.1 times higher than for bicyclists under age 16. The relative risk of fatality was even higher for riders over the age of 44, and was highest for those over age 64. Riders over age 64 were about 3.2 times more likely to be involved in fatal accidents than 16-to-24 year-old riders, and about 6.6 times more likely to be involved in fatal accidents than riders under age 15. Finally, riding after dark appears to contribute to the fatality risk. An estimated 23.5 percent of the deaths occurred between the hours of 9:00 p.m. and 5:59 a.m. Although daylight conditions vary during the year and by region, most of these deaths probably occurred after dark. Another 22.9 percent of the deaths occurred between 6:00 p.m. and 8:59 p.m., some of which probably occurred after dark. In contrast, only about 12.4 percent of riders from the exposure survey reported that they engage in nighttime riding at least some of the time. Nighttime riding therefore appears to be an important contributing factor in bicycle deaths. Bicycle Helmet Findings While recent studies show substantial safety benefits from helmet use, they also reveal that only a small proportion of riders actually use helmets. The exposure survey provides valuable insights into current helmet usage patterns and on the reasons why riders use or do not use helmets. This section summarizes the helmet usage patterns of bicyclists and the statistical analysis of factors associated with helmet use, which are detailed in Part II. It also describes the attempt in Part III to evaluate the impact of helmet use on the likelihood of head injury. Descriptive Results The exposure survey found that only 11.8 million (18 percent) of the entire population of about 67 million bicyclists wear helmets all or most of the time. Another 6 percent, representing about 4 million riders, reported that they wear helmets sometimes, but less than half of the time. The proportion of children under age 15 who wear helmets all or most of the time was about 15 percent. HF reports (in Part IV) that the low usage rate for children may be partly related to peer pressure. Some studies show that children are not inclined to wear helmets if 11

12 their social group disapproves of helmet use. However, helmet use in all age groups appears to be increasing. Just over half of the current users (53 percent) began wearing helmets in the last two years. 6 Nearly all of the 9 million riders who always wear helmets described "safety" as an important reason for doing so. The "insistence of family members," was also important to about half of those who always wear helmets. Usage patterns for 6.8 million riders who wear helmets sometimes, but not all of the time, are apparently affected by risk perceptions. Many said that they usually wear helmets when in traffic (40 percent) and when on long rides (25 percent). Many also reported that they are less likely to wear helmets when riding only a short distance and when not riding in traffic. Finally, when non-helmet users were asked why they do not wear helmets, nearly half (48 percent) reported that they had never considered wearing helmets, 21 percent said helmets were unnecessary, 19 percent said they did not wear helmets because they seldom ride in traffic, and 16 percent said they had not gotten around to wearing them. Helmet Use Patterns In an analysis of factors associated with helmet use, the exposure survey data revealed that the likelihood of helmet use increases with the amount of riding time. It is higher for those who ride on major thoroughfares and bike paths, and is lower for those who ride on neighborhood streets and on sidewalks and playgrounds. The relationship between age and helmet use is more complex, suggesting that helmet use increases with age for frequent riders and declines with age for infrequent riders. The results also suggest that children age 10 and under are more likely to wear helmets, relative to older riders, than can be otherwise explained by the general relationship between age and risk. The likely explanation is that enough parents of young children require their children to wear helmets so that helmet use patterns of children are distinguished from those of older bicyclists. Helmet use also increases substantially with higher household education levels. These relationships are illustrated for individual riders in a table at page 53. For example, consider a male who rides 300 hours per year on neighborhood streets, and who has (or, for children, whose parents have) no more than a high school education. The expected likelihood of helmet use decreases from 9.9 percent for a 10 year-old rider to 6.8 percent for a 20 year-old rider. However, it rises again to 10.5 percent for a 40 year-old rider. In contrast, for a 30 year-old female who rides about 50 hours a year on neighborhood streets, the 6 The Rodale Press findings for adults, described in Part VII, were similar. In 1990, only about 15 percent of adult bicyclists wore helmets all or some of the time. However, the results also suggested that helmet use was likely to increase substantially. About 10 percent of riders who did not own helmets said they planned to buy one within 2 years. If plans materialized, helmet usage rates would have increased to about 25 percent by

13 likelihood of helmet use rises from 5.4 percent if she has a high school education, to 16.4 percent if she has a college education. It rises further to 37.1 percent if she not only has a college education but also rides primarily on major thoroughfares. The analysis of the Rodale Press survey data on helmet usage patterns (in Part VIII) came to similar conclusions. Helmet use increased with riding distances, and was higher for bicyclists who ride primarily on major thoroughfares and off-road trails. In addition, helmet use increased with household income, a variable not included in the analysis of helmet use patterns from the exposure survey. Helmet Effectiveness Since helmets are intended to reduce the likelihood of head injury, EP used injury survey data to examine the safety effects of helmet use by estimating the conditional probability of head injury given that a helmet was worn. As described in Part III, the results of this analysis were inconclusive, probably because the sample of helmet users was small (only about 12 percent of the injured riders were wearing a helmet at the time of accident), and possibly because no information was available on riders who avoided injuries or whose injuries were less severe because they were wearing helmets. However, EP found evidence that helmets prevented or reduced the severity of some head injuries. Helmets were damaged in 16 of the injury cases, about one-third of the cases in which they were worn. In 11 of these cases (69 percent), the victim did not sustain a head injury. In addition, in all 16 cases, the victim expressed the opinion that the helmet prevented a head injury or made it less severe. Conclusions and Implications for Injury Reduction The bicycle study documented the large number of bicycle-related injuries and deaths that occur every year, and evaluated the use and hazard patterns of bicyclists in the United States. While the costs to society of bicycle-related injuries and deaths are enormous -- on the order of $8 billion annually -- the bicycle study does not indicate any simple or direct remedies to the hazards of bicycle riding. Bicycle accidents result from a complex interaction of behavioral, environmental, and mechanical factors. Efforts to reduce injuries must therefore be based on long term strategies which systematically address risk factors on a number of fronts at the same time. The behavioral factors leading to injuries, for example, might be addressed by training, or by strategies that make riders aware of safe riding practices and the consequences of unsafe riding practices. Environmental factors might be addressed by improving road design, or by promoting the development of bike lanes and bike paths. Similarly, mechanical factors might be addressed by product modification. In addition, all of these factors may be addressed by the use of safety equipment which prevents or mitigates the severity of injury when accidents occur. 13

14 Although the bicycle study could not quantify the causal relationship between the behavioral, environmental, and mechanical factors and the injury risk, the study's results indicate that the behavioral factors constitute an important component. A large proportion of bicycle injuries result from behaviors which are risky or reflect poor riding judgment (e.g., stunting or riding too fast given the riding conditions). In addition, the cognitive and physical immaturities of children are likely contributing factors in many of their injuries. The bicycle study also found that environmental factors, such as riding terrain and riding conditions, play an important role in the injury risk. On the other hand, while poor bicycle maintenance was a hazard factor, the structure of the bicycle itself appeared to play little role in the injury risk. The remainder of this section discusses these general conclusions, and their implications for injury reduction. Mechanical Factors One purpose of the bicycle project was to determine whether there are significant mechanical failure patterns that warrant amendments or revisions to the existing mandatory standard for bicycles. Although there was no reason at the outset of the project to believe that revisions were necessary, possible mechanical hazard patterns have not been evaluated on a systematic basis since the standard went into effect almost 20 years ago. In addition, changes in the bicycle market (such as the availability of mountain bikes) may have resulted in new mechanical hazard patterns not envisioned in the original standard. The bicycle study, however, provides no evidence that any bicycle type (e.g., lightweight racing, BMX, mountain, etc.) is inherently more hazardous than any other. Hazard patterns involving bicycle types were found to be related primarily to the age and riding patterns of users. In addition, the ES review of the injury data found no evidence of systematic mechanical hazards that would warrant amendments or revisions to the existing mandatory standard for bicycles. Although mechanical failure was identified as a possible contributing factor in as many as 13 percent of the injury reports, ES concluded that a large proportion of these injuries involved poor bicycle maintenance and/or bicycle modifications, as well as external riding conditions such as wet, slippery riding surfaces. Because of the findings concerning bicycle maintenance and modification, ES recommends that both adults and children be made aware of the importance of maintaining a bicycle in good working condition and of the risks of modifying a bicycle. Environmental Factors The risk analysis revealed a substantial risk differential between paved roadways (which are shared with motor vehicles) and bike paths (which are generally shared with other bicycles, joggers, walkers, and skaters). When holding other factors statistically constant, the risk of injury on neighborhood streets was about seven to eight times the risk on bike paths, and the 14

15 risk on major thoroughfares was even greater than on neighborhood streets. Moreover, about 90 percent of bicyclist deaths involve crashes with motor vehicles on public roadways. These findings suggest that the riding environment should be an important focus of efforts to reduce bicycle injuries and deaths. Such efforts might focus on improvements in roadway design aimed at reducing many of the serious injuries involving collisions with automobiles every year. The development of bike paths (i.e., paths that separate bicycles from parallel motor vehicle traffic) and bike lanes (i.e., designated lanes on roadways which are offlimits to motor vehicles) should also be considered. Efforts to improve the bicycle riding environment are already underway at all levels of government. As mentioned above, the DOT's 1991 Appropriations Act instructed DOT to develop a plan to promote bicycling and walking, and to enhance the safety of these transportation modes. The goals of the plan are to double the percentage of trips made by bicycling and walking by the year 2000, and to simultaneously reduce by 10 percent the number of bicyclists and pedestrians killed or injured in traffic crashes (Federal Highway Administration, 1994). DOT hopes to do this by, among other things, promoting the use of federal funds for the development of a bicycle-friendly infrastructure (i.e., riding surfaces, lighting at night, and facilities), and for education and training. The Intermodal Surface Transportation Efficiency Act (ISTEA) also promotes improvements in the riding environment. ISTEA requires that all state and local governments incorporate programs and facilities for bicyclists in transportation plans. ISTEA also requires states to establish and fund bicycle and pedestrian coordinator positions for promoting and facilitating the increased use of nonmotorized modes of transportation. The higher injury risk on roadways also suggests that motorists and bicyclists need to be educated in bicycle safety. Motorists need to be aware of the many road hazards that confront bicyclists, to help them avoid collisions when approaching bicyclists on the road. Being aware of road hazards confronting bicyclists can also help them better assess high risk areas, such as intersections, and be more attentive in areas where bicyclists may not be clearly in view. Safety programs geared toward adult bicyclists who ride in traffic, such as the League of American Bicyclist's hands-on training program "Effective Cycling," should also be encouraged. Behavioral Factors The bicycle study found that many of the bicycle-related injuries and deaths every year are related to what the rider does and how the rider interacts with environmental factors. Riding practices that are risky, that reflect poor riding judgment, or that fail to account for environmental conditions, play a major role in injury and fatality scenarios. This finding suggests that information and education (I&E) might play a role in injury reduction. Many groups and organizations, including the CPSC, actively promote bicycle safety through informational efforts. The promotion of bicycle safety through public service 15

16 announcements, brochures, poster campaigns, and other means must continue. These messages reach new audiences and reinforce safety behavior. However, I&E efforts, particularly those which are short term or do not present new information to consumers, may have limited additional impact on rider behavior. Moreover, information by itself is unlikely to change the behavior of children. One of the most striking findings of the study is the higher risk of injury for children. About 71 percent of the emergency room treated injuries, and 37 percent of the deaths involved children under age 15. In addition, when other factors are held statistically constant, the expected injury risk for a child under age 15 is over 5 times the risk for an older rider. A clear implication is that there is a potentially big injury reduction payoff that may be gained by focusing on the behavior of the highest risk population, children. One remedy is to train children in safe riding practices. Child training programs need to be developed judiciously. From a review of the available bicycle training literature, HF finds a consensus among child development experts that many safety concepts cannot be learned by children before a certain maturational level, regardless of the amount of training. In large part, this is because of children's physical and cognitive limitations in dealing with a complex and constantly changing riding environment. Determining the time appropriate to begin bicycle safety education is therefore essential in designing effective programs. Existing behavioral studies find that the optimal time for intensive bicycle safety education for children is between the third and sixth grades (i.e., riders 9 to 12 years of age). (See references in Part IV.) This does not mean that younger children should not have any type of training, but that a comprehensive program is most effective beginning in the third or fourth grades, with refresher courses for older children and adults. By the sixth grade, most children have the ability to understand and perform the taught behaviors. The analysis of risk and hazard patterns reveals several areas that should be stressed in training programs for children. Helmet use should be encouraged to reduce the incidence of head injury, which was especially high for children. Roadway skills should be emphasized, as indicated by the substantially higher risks on streets. The higher risks during non-daylight hours indicate that night riding by children should be discouraged. Training courses should also include some basic information on how to maintain bicycles in good working order. It would also be useful to convey child safety information to parents who, if they were aware of risks, might encourage safer riding habits, such as the use of helmets. Given children's risk patterns and available human factors information on the cognitive and physical development of children, parents might want to discourage or prohibit children under the age of about 10 from riding on roadways (without direct parental supervision) or from riding at all during non-daylight hours. 16

17 Other Implications: Safety Equipment The importance of the behavioral and environmental factors in hazard patterns also has implications for the use of protective safety equipment, which can prevent or mitigate injuries when accidents occur. Encouraging children to use safety equipment, such as helmets, is especially important because of the difficulty in teaching young children certain safety skills. Head injuries represent the most serious and potentially life threatening injuries that can be sustained by bicyclists. According to the injury survey results, almost one-third of hospital emergency room treated injuries involve the head, and children under age 10 are significantly more likely than older riders to suffer head injuries. In addition, Sacks et al. (1991) estimate that about 62 percent of all U.S. bicycle-related deaths involve injuries to the head. Based on these estimates, the societal costs associated with the bicycle-related injuries and deaths involving head injury amounted to more than $3 billion in Available evidence indicates that helmets reduce both the likelihood and severity of head injury (Dorsch et al, 1987; Thompson et al., 1989). Results from the exposure survey, however, indicate that only about 17.6 percent of bicyclists currently wear helmets. This is higher than the 5 to 10 percent usage rate estimated in studies conducted only a few years ago (see references at Part II), and suggests that attitudes towards helmet use are improving. Nevertheless, helmet usage rates remain low. Increasing helmet use may therefore be the single most important factor in reducing the incidence of serious bicycle injuries. The high incidence of fatal accidents after dark also suggests night riding is an area for future safety efforts. People who ride at night should be aware of the need to see and be seen. This suggests that the use of bicycle headlights and reflective clothing should be encouraged. Night riders should also make sure that their bicycles are equipped with reflectors, as required by the CPSC bicycle standard. 17

18 References Bicycle Institute of America. Bicycling Reference Book: Transportation issue. Washington, DC: Author; Cross, K. D., and Fisher, G. A study of bicycle/motor-vehicle accidents: Identification of problem types and countermeasure approaches (Technical Report DOT-HS ). Washington, DC: National Highway Traffic Safety Administration; Dorsch, Margaret M.; Woodward, Alistair J.; Somers, Ronald L. Do bicycle safety helmets reduce severity of head injury in real crashes? Accident Analysis and Prevention 19(3): ; Federal Highway Administration. National Bicycling and Walking Study. (Technical Report FHWA-PD ), Washington, DC: Author; National Sporting Goods Association. Sports participation in Mt. Prospect, Ill.: Author; Rodale Press. The cycling consumer of the 90's: A comprehensive report on the U.S. adult cycling market. Emmaus, PA: Author; Roland, H.E., Hunter, W.W., Stewart, J.R., and Campbell, B.J. Investigation of motor vehicle/bicycle collision parameters (Technical Report DOT-HS ). Washington, DC: National Highway Traffic Safety Administration; Sacks, J.J.; Holmgreen, P.; Smith, S.M.; and Sosin, D.M. Bicycle-associated head injuries and deaths in the United States from 1984 through 1988: How many are preventable. Journal of the American Medical Association 266(21): ; December 4, Thompson, Robert S; Rivara, Frederick P.; Thompson, Diane C. A case control study of the effectiveness of bicycle safety helmets. The New England Journal of Medicine 320(21): ; May 25,

19 Part II. Bicycle and Bicycle Helmet Use Patterns in the United States: A Description and Analysis of National Survey Data Gregory B. Rodgers, Ph.D. Directorate for Economic Analysis November 1992 Introduction Bicycle riding is an important means of transportation, as well as one of the most popular recreational activities in the United States (National Sporting Goods Association, 1992). This popularity is accompanied by a large number of injuries and deaths every year. Based on data from the U.S. Consumer Product Safety Commission's (CPSC) National Electronic Injury Surveillance System (NEISS), a stratified random sample of U.S. hospital emergency rooms (CPSC, 1988), there are more than an estimated 500,000 nonfatal bicyclerelated injuries treated in the nation's hospital emergency rooms annually. When other medically-attended injuries are counted, such as injuries treated in physicians' offices, there may be on the order of about one million medically-attended injuries involving bicycles every year (J. Robb Associates, 1976). In addition, based on information from the National Safety Council (1992), there are almost 1,000 bicycle-related deaths annually. The societal costs of bicycle-related injuries and deaths are large. Based on the CPSC's Injury Cost Model (Technology & Economics, 1980), the costs of the medicallyattended injuries amount to about $6 billion annually. In addition, based on an imputed cost of $2 million per life lost, fatalities add $2 billion annually. The total estimated societal costs of bicycle-related injuries and deaths may therefore be about $8 billion annually. In spite of the large number of injuries and deaths, there has never been a comprehensive national survey designed to gather information on the characteristics and use patterns of the general population of bicyclists. 1 The published literature on bicycle hazards consists primarily of injury analyses, most of which have been carried out at the level of the 1 Rodale Press recently conducted a major survey of adult bicycle riders in the United States (Rodale Press, 1991). However, the Rodale Press survey was limited to bicycle riders age 18 and older who had acquired new bicycles, and accounts for only about 60 percent of all U.S. bicycle riders. 19

20 individual hospital or in limited geographical areas. Several recent studies have also attempted to measure the effectiveness of helmets in reducing head injuries. Injury studies provide valuable information about injury characteristics and scenarios. However, in the absence of control (or "exposure") data describing the characteristics and use patterns of the rider population, injury studies are not enough to allow us to quantify the injury and fatality risks associated with bicycle use (Dewer, 1978; HDR Engineering, 1991). 2 This report presents the results of a comprehensive, nationwide 1991 survey of U.S. bicycle riders (the "exposure survey") conducted by the U.S. Consumer Product Safety Commission. It provides information on: the number of riders and bicycles in use; the demographic characteristics of rider households; rider characteristics and use patterns; helmet use patterns; and the types of bicycles in use. The report also presents an analysis of the factors associated with helmet use. These factors are determined and quantified with a probit regression model, a qualitative response model that can be used to estimate helmet use probabilities for individual bicyclists and for various population subgroups. Survey Methodology Abt Associates, Inc. ("Abt"), a survey firm located in Cambridge, Massachusetts, designed for the CPSC a telephone survey to provide a national probability sample of households with bicycle riders in the 48 contiguous states and the District of Columbia. The survey used the Mitofsky-Waksberg method of random-digit-dialing (Waksberg, 1978), a two-stage sampling procedure intended to give all telephone numbers in the continental U.S. an equal probability of selection. The survey's initial goal was to complete about 1,150 interviews with bicycle riders from around the nation. A detailed description of the sampling procedure is provided in the appendix. 2 Consider an example. About 70 percent of nonfatal injuries treated in hospital emergency rooms involve children under the age of 15 (Tinsworth, 1987). However, there are no nationwide data describing the riding patterns and behaviors of these children, or the amount of riding they engage in. This makes it difficult to determine whether the large proportion of injuries suffered by children results from high levels of exposure (i.e., aggregate riding times), risky riding patterns, or limitations in motor or cognitive skills. Exposure information, as well as injury information, is needed to evaluate these risks, to determine the relative importance of the various hazard patterns, and, ultimately, to develop effective intervention strategies to reduce injuries. 20